Tomy S, Wu G-C, Huang H-R, Dufour S, Chang C-F
Department of Aquaculture, National Taiwan Ocean University, Keelung, Taiwan.
J Neuroendocrinol. 2007 Aug;19(8):643-55. doi: 10.1111/j.1365-2826.2007.01572.x.
In the present study, we tested the hypothesis that the brain of the black porgy fish, Acanthopagrus schlegeli, has the capacity for de novo steroidogenesis and that these neurosteroids may impact sex differentiation. Gonadal histology and Dmrt1 gene expression revealed that the fish were not sex differentiated until 155 dah (days after hatching). We further demonstrated the developmental expressions of the mRNAs encoding for four key neurosteroidogenic enzymes, namely, the cytochrome P450 side chain cleavage (CYP11A1), 3beta-hydroxysteroid dehydrogenase/Delta(5)-Delta(4) isomerase (3betaHSD), cytochrome P450c17 (CYP17) and aromatase (CYP19b) in the brain at different post-hatching developmental ages. The results indicated that steroidogenic genes are expressed in brain from the earliest sampling time, 60 dah. Quantitative real-time polymerase chain reaction analysis demonstrated significantly higher expression levels of these enzymes at 120 dah compared to 60 dah in all the brain regions. However, the increase for 3betaHSD was significant only in hypothalamus and midbrain, whereas it was significant only in forebrain and hypothalamus for CYP19b. A decline in mRNA levels were observed for all the genes at 155 dah except in midbrain for CYP11A1 and in hindbrain for CYP19b. Analysis of aromatase enzyme activity showed a significant increase in aromatase activity in the forebrain at 120 dah. Thus, the present study demonstrated for the first time an age- and/or region dependent expression of the mRNAs encoding the steroidogenic enzyme genes in the brain of black porgy. The presence of key steroidogenic enzymes as early as 60 dah, before gonadal sex differentiation, demonstrates that steroid biosynthetic capacity in brain precedes histological gonad differentiation. The mRNA transcripts of these genes showed a synchronous peak at 120 dah, suggesting that oestradiol may be locally formed in most parts of the brain. The study suggests an important role for brain aromatase in male black porgy brain sex differentiation, and considers the possibility of a role for this enzyme in neurogenesis.
在本研究中，我们验证了以下假设：黑鲷（Acanthopagrus schlegeli）的大脑具有从头合成类固醇的能力，并且这些神经类固醇可能会影响性别分化。性腺组织学和Dmrt1基因表达显示，这些鱼直到孵化后155天（dah）才发生性别分化。我们进一步证明了在不同孵化后发育阶段，大脑中编码四种关键神经类固醇生成酶的mRNA的发育表达情况，这四种酶分别是细胞色素P450侧链裂解酶（CYP11A1）、3β-羟基类固醇脱氢酶/Δ5-Δ4异构酶（3βHSD）、细胞色素P450c17（CYP17）和芳香化酶（CYP19b）。结果表明，从最早的采样时间（60 dah）起，类固醇生成基因就在大脑中表达。定量实时聚合酶链反应分析表明，与60 dah相比，在120 dah时所有脑区中这些酶的表达水平均显著更高。然而，3βHSD的增加仅在下丘脑和中脑显著，而CYP19b的增加仅在前脑和下丘脑显著。在155 dah时，除了中脑中的CYP11A1和后脑中的CYP19b外，所有基因的mRNA水平均出现下降。芳香化酶活性分析显示，在120 dah时前脑的芳香化酶活性显著增加。因此，本研究首次证明了黑鲷大脑中编码类固醇生成酶基因的mRNA存在年龄和/或区域依赖性表达。早在性腺性别分化之前的60 dah就存在关键的类固醇生成酶，这表明大脑中的类固醇生物合成能力先于性腺组织学分化。这些基因的mRNA转录本在120 dah时出现同步峰值，表明雌二醇可能在大脑的大部分区域局部形成。该研究表明大脑芳香化酶在雄性黑鲷大脑性别分化中起重要作用，并考虑了这种酶在神经发生中发挥作用的可能性。
